A fuel cell is defined as a primary electrochemical cell using the oxidation of fossil fuels or their derivatives by oxygen as the energy source. A fuel cell thus is a continuous-feed electrochemical cell in which energy from such a reaction is converted directly to electrical energy as long as fuel and oxygen are provided.
A fuel cell has an inherently high energy efficiency, as much as 85% in practice, as it converts chemical energy potential directly to electricity, avoiding the thermodynamic inefficiency of the Carnot cycle associated with heat engines. The practical difficulties of limited catalyst and electrode lives, the need for pure reactants, and engineering and fabrication difficulties and expense have all retarded development, installation, and use of fuel cells.
The most highly developed cells use a phosphoric acid electrolyte, a hydrogen-rich mixture of fuel gases obtained via the reforming action with steam, porous carbon or graphite electrodes and cell separators, with platinum group metal catalysts, operating at elevated temperatures (up to 200.degree. C.) and pressures. The problems of confining a gaseous fuel and a corrosive electrolyte at such conditions, avoiding catalyst poisoning (principally due to sulfur compounds) and limited electrode life have prevented large-scale use of fuel cells to the present time.
Past efforts in the field have resulted in U.S. Pat. No. 3,867,206, Trocciola et al., disclosing a fuel cell having an electrolyte saturated matrix between electrodes sealing the gas by hydrophilic capillary action; U.S. Pat. No. 4,035,551, Grevstad, discloses a fuel cell having a porous electrolyte retaining matrix separating the electrodes with graduated pore sizes totally hydrophilic to the electrolyte; U.S. Pat. No. 4,115,528, Christner et al., discloses a method for fabricating porous carbon sheet material for fuel cell electrode substrates comprising coating carbon fibers with a mixture of furfuryl alcohol and a catalyst, with phosphoric acid the preferred catalyst, heating the mat to polymerize the furfuryl alcohol, and further heating at 1500.degree. C. to carbonize the resin; U.S. Pat. No. 4,115,627, Christner, discloses a ribbed electrode substrate for an electrochemical cell having ribs of hydrophilic material on one side and optionally coated on the other side with a catalyst layer; U.S. Pat. No. 4,165,349, Sandelli, discloses a method for fabricating a porous ribbed electrochemical cell substrate comprising molding the substrate by loading a die with a dry mixture of thermosetting resin and carbon fibers, curing the mixture, then heating to 1100.degree. C. to convert the resin to glassy carbon having a porosity of at least 75%; U.S. Pat. No. 4,233,369, Breault et al., discloses a cooler assembly for a stack of fuel cells comprising a fibrous, porous coolant tube holder sandwiched between and bonded to at least one of a pair of gas impervious graphite plates. Gas seals along the edges of the holder parallel to the channels are gas impervious graphite strips; U.S. Pat. No. 4,245,009, Guthrie, discloses a coolant tube holder for a stack of fuel cells, a gas porous sheet of fibrous material sandwiched between a cell electrode and a nonporous, gas impervious flat plate which separates adjacent cells. The porous holder has channels in one surface with coolant tubes. The gas impervious plate is bonded to the opposite surface of the holder, and the channel depth is the full thickness of the holder; U.S. Pat. Nos. 4,269,642 and 4,365,008, DeCasperis, disclose densified edge seals for fuel cell components comprising a porous electrode having a densified edge made from the same composition as the rest of the component bY compressing an increased thickness of the material along the sides during the fabrication process, and a method for producing same; U.S. Pat. No. 4,422,894, Atkinson et al., discloses a flat gasket incorporating a metallic reinforcement layer formed by pressing uncompacted expanded graphite onto the opposed faces of the reinforcement simultaneously to form compacted graphite foils in situ while at the same time pressing some of the graphite particles relative to one edge to form a single unreinforced graphite foil portion extending from and integral with the other foils to enclose that one edge; U.S. Pat. No. 4,165,349, Sandelli, discloses a method for fabricating a porous electrochemical cell by loading a die with a dry mixture of thermosetting resin and carbon fibers, heating and curing up to 300.degree. C. See also Enc. of Chem. Tech., Kirk-Othmer 3rd Ed., Vol. 3, pp. 545-568.